Various types of customizable integrated circuits and programmable integrated circuits are known in the art. Customizable integrated circuits include gate arrays, such as laser programmable gate arrays, commonly known as LPGA devices, which are described, inter alia in the following U.S. Pat. Nos. 4,924,287; 4,960,729; 4,933,738; 5,111,273; 5,260,597; 5,329,152; 5,565,758; 5,619,062; 5,679,967; 5,684,412; 5,751,165; 5,818,728. Devices of this type are customized by etching or laser ablation of metal portions thereof.
There are also known field programmable gate arrays, commonly known as FPGA devices, programmable logic devices, commonly known as PLD devices, as well as complex programmable logic devices, commonly known as CPLD devices. Devices of these types are programmable by application of electrical signals thereto.
It has been appreciated in the prior art that due to the relatively high silicon real estate requirements of FPGA devices, they are not suitable for many high volume applications. It has therefore been proposed to design functional equivalents to specific programmed FPGA circuits. Such functional equivalents have been implemented in certain cases using conventional gate arrays. The following U.S. Patents show such implementations: U.S. Pat. Nos. 5,068,063; 5,526,278 & 5,550,839.
Programmable logic devices are known in which programmable look up tables are employed to perform relatively elementary logic functions. Examples of such devices appear in U.S. Pat. Nos. 3,473,160 and 4,706,216. Multiplexers are also known to be used as programmable logic elements. Examples of such devices appear in U.S. Pat. Nos. 4,910,417, 5,341,041 and 5,781,033. U.S. Pat. Nos. 5,684,412, 5,751,165 and 5,861,641 show the use of multiplexers to perform customizable logic functions.
Problems of clock skew in gate arrays are well known. U.S. Pat. No. 5,420,544 describes a technique for reducing clock skew in gate arrays which employs a plurality of phase adjusting devices for adjusting the phase at various locations in gate arrays. Various clock tree design structures have been proposed which produce relatively low clock skew.
PCT Published Patent Application WO 98/43353 describes a functional block architecture for a gate array.
U.S. Pat. Nos. 5,825,202 and 5,959,466 describes an integrated semiconductor device comprising a FPGA portion connected to a mask-defined application specific logic area.
Various types of gate arrays are well known in the art. Gate arrays comprise a multiplicity of transistors, which are prefabricated. A specific application is achieved by customizing interconnections between the transistors.
Routing arrangements have been proposed for reducing the number of custom masks and the time needed to manufacture gate arrays by prefabricating some of the interconnection layers in two-metal layer gate array devices. Prior art devices of this type typically employ three custom masks, one each for the first metal layer, via layer and second metal layer.
U.S. Pat. No. 4,197,555 to Uehara describes a two-metal layer gate array device wherein the first and second metal layers are pre-fabricated and the via layer is customized. Uehara also shows use of pre-fabricated first metal and via layers and customization of the second metal layer.
U.S. Pat. Nos. 4,933,738; 5,260,597 and 5,049,969 describe a gate array which is customized by forming links in one or two prefabricated metal layers of a two-metal layer device.
U.S. Pat. No. 5,404,033 shows customization of a second metal layer of a two-metal layer device.
U.S. Pat. No. 5,581,098 describes a gate array routing structure for a two-metal layer device wherein only the via layer and the second metal layer are customized by the use of a mask.
Dual mode usage of Look-Up-Table SRAM cell to provide either a logic function or memory function has been proposed for FPGA devices in U.S. Pat. Nos. 5,801,547, 5,432,719 and 5,343,403.
Programmable and customizable logic arrays, such as gate arrays, are well known and commercially available in various sizes and at various levels of complexity. Recently cores of such logic arrays have become available.
Conventionally, cores are provided by a vendor based on customer's specifications of gate capacity, numbers of input/output interfaces and aspect ratio. Each core is typically compiled by the vendor for the individual customer order. Even though the cores employ modular components, the compilation of the cores requires skilled technical support and is a source of possible errors.
Examples of prior art proposals which are relevant to this technology include Laser-programmable System Chips (LPSC), commercially available from Lucent Technologies Inc., and Programmable Logic Device (PLD) cores, commercially available from Integrated Circuit Technology Corp. of California.
Integrated circuits are prone to errors. The errors may originate in the design of an integrated circuit in a logically incorrect manner, or from faulty implementation.
A debugging process is required to detect these errors but fault-finding is a difficult process in integrated circuit devices due to the inaccessibility of the individual gates and logic blocks within the integrated circuit device.
The designer needs an apparatus and method for observing the behavior of an integrated circuit device, while the device is in its "working environment". Furthermore, in order to isolate and determine a faulty area or section of an integrated circuit device, a designer needs to be able to control the inputs to the faulty area or section (controllability), and also to be able to observe the output from the faulty area (observability). In a typical integrated circuit device, controllability and observability are severely limited due to the inaccessibility of the device and the sequential nature of the logic.
The prior art teaches methods for enhancing the controllability and the observability of an integrated circuit device. A method suggested by Eichelberger et al., in "A Logic Design Structure for LSI Testability", Proceeding of the 14.sup.th Design Automation Conference, June 1977, is to use a "scan chain" method. In this method of Eichelberger, storage elements are tied together in one or more chains. Each of these chains is tied to a primary integrated circuit pin. Special test clocks allow arbitrary data to be entered and scanned in the storage elements independent of the device's normal function.
The following U.S. patents are believed to represent the current state of the art: U.S. Pat. Nos. 5,179,534; 5,157,627, and 5,495,486.
Semiconductor devices, such as ASICs, have traditionally been manufactured by ASIC design and fabrication houses having both ASIC design and fabrication capabilities. Recently, however, the design and fabrication functionalities have become bifurcated, such that a customer may bring his fab-ready design to a fabrication house, having no design capability. The customer may employ conventionally available cell libraries, such as those available, for example, from Artisan or Mentor Graphics together with known design rules, to design their own devices.
Semiconductor design modules having specific functions, known as cores, are also available for integration by a customer into his design. An example of a commercially available core is a CPU core, commercially available from ARM Ltd. of Cambridge, England.
Cores may be provided in a variety of forms. For example, a "soft core" may be in the form of a high level schematic, termed RTL, while a "hard core" may be at a layout level and be designed to specific fabrication design rules.
Conventional ASIC design flow is based on the use of synthesis software that assists a design-engineer to convert the design from high-level description code (RTL) to the level of gate netlist. Such a software tool is available from Synopsys Inc., 700 E. Middlefield, Mountain View, Calif., USA, and commercially available under the name of "Design Compiler". While software tools, such as "Design Compiler" are highly complex, they are limited by, for example, the number of logic functions, called "Library Functions", which may be used for gate level implementation.
For example, "Design Compiler" can use up to about 1,000 logic functions. This relatively small number of logic functions limits the usefulness of "Design Compiler" with eCells. The term "eCell" is defined hereinbelow. A typical eCell may be configured to perform more than 32,000 different logic functions.
Therefore there is a necessity in the art to provide a tool for synthesizing an eCell.